The present invention relates to an improved spinal surgical prosthesis and more particularly to apparatus and methods for achieving stability of adjacent vertebrae and preserving the inter-disc space following disectomy by internal fixation or fusion.
Fusion commonly performed for adjacent bone structures and those not adjacent provides for long term replacement as a result of degenerative or deteriorated disorders in bone.
An inter-vertebral disc is a ligamentous cushion disposed between vertebrae and as a result of injury, disease or other disorders may deteriorate in part or in whole, thereby leading to mechanical instability and painful disc translocations and often necessitating bed rest or hospitalization. If left untreated possible subsequent involvement of adjacent nerves and muscular involvement may occur. In such cases, if treatment is delayed, permanent damage to the nerves may result in muscular atrophy and severe dysfunction.
Procedures for disc surgery may involve partial or total excision of the injured disc portion and replacement with biocompatible devices of bone or bone-like material.
Bone material was simply disposed between the adjacent vertebrae, typically at the posterior aspect of the vertebrae and the spinal column was stabilized by way of a plate or rod connecting the involved vertebrae. However, the use of bone may require undesired additional surgery and is of limited availability in its most useful form. In addition, the risk of infection and rejection is a significant consequence. In any event, bone is only marginally structural and with bone it is difficult to stabilize both the implant against dislodgment and stabilize the adjacent vertebrae. It becomes desirable to find solutions for stabilization of an excised disc space by fusing the vertebrae between their respective end plates without the need for anterior or posterior plating or rods.
A review of the prior art clearly reveals attempts to achieve such solutions in two distinct areas, namely:
I. Static inter-body fusion devices
II. Adjustable inter-body fusion devices that can restore and stabilize varying heights of the intra-discal space.
I. Static Inter-body Fusion Devices
An extensive number of static inter-body fusion devices commonly called xe2x80x9ccagesxe2x80x9d have evolved for replacement of a damaged disc while still maintaining stability of the disc inter-space between the adjacent vertebrae.
However, existing static inter-body fusion devices encountered some problems. They require drilling, boring or tapping of the end plates which sometimes results in removal of an excessive amount of supporting bone with possible damage to adjacent structures. Moreover, threads of the implant or cage may inadvertently engage the prepared threads of the vertebrae in an improper manner so as to cause a misalignment of the vertebrae in an anterior-posterior direction as well as laterally. If a second cage is needed, it involves the drilling, boring or tapping of the vertebral end plates for both cages so that the threads direct the cages into their proper respective positions. Such preparation requires highly skilled precision that may not be afforded or attainable under normal working conditions.
When a second cage is inserted, due to the unevenness of the vertebral end plates concave engaging surfaces, an unwanted increase in the inter-vertebral space may result in the loosening and possible dislodgment of the initially placed implant cage.
The anatomical configurations of the vertebrae necessitates that the two cages be positioned at an angle in respect to each other so as to be totally within the confines of the lateral borders of the vertebrae involved.
Use of tapered cages that are dimensionally greater in height anteriorally than posteriorally so as to provide the proper lordosis when such cage implants are employed creates complications. When the posterior approach is utilized and drilling, boring or tapping is necessary for placing threads on the vertebral end plates, difficulties exist in creating threads that will have a pitch compatible with those exhibited by the threads of such cages. A further complication is present when utilizing tapered cages via the posterior approach in that the dimensionally higher anterior threaded portion of the tapered cage is initially inserted and advanced to its most anterior final resting position. These cages are self-tapping to some degree and may result in the unwanted excessive removal of bone from the posterior portion of the lumbar segments where the lordosis is greatest.
Drilling and other types of preparation of the vertebral end plates may result in the removal of excessive amounts of supporting bone, and may cause the cage implants to rest upon the cancellous portion of the vertebrae. In such instances the cages may settle into said vertebrae resulting in a decreased inter-vertebral space other than that desired with subsequent complications of stabilization, pain and discomfort.
II. Adjustable Inter-body Fusion Devices
These are designed for restoring and maintaining the inter-vertebral space thereby providing for the normal contour of the fused spinal segments. Once the disc is removed, the normal lordotic or kyphotic curvature is eliminated and adjustable inter-body fusion implants are employed for re-establishing the proper curvature and stabilization of the spine.
Adjustable inter-body fusion devices have universal applicability and may eliminate the need for surgical preparation of the vertebral end plates such as contouring of bone and drilling, boring and tapping of said vertebral end plates. Such devices restore and preserve the inter-space and the integrity of the adjacent vertebrae thereby making the selection of the proper implant easier. They result in preservation of the highly specialized weight bearing cortical bone thereby preventing end plate perforation into the highly vascular cancellous bone marrow and unwanted subsequent bleeding may result in many complications due to excessive blood loss risks (e.g. hypoglycemic shock, transfusion, and possible diseases such as hepatitis and Acquired Immune Deficiency Syndrome, etc.),. Another advantage of such devices is the elimination of incorrect implant size selection as no significant amount of bone is removed and the correct size implants are easily fitted to restore the proper inter-space. In addition, the implant is self-stabilizing without the use of threads and may be further enhanced by surface treating of the implant for bone in-growth and osseous integration of the implant.
The following patents disclose Static Inter-Body Fusion Devices: U.S. Pat. Nos. 5,785,710; 5,782,919; 5,766,253; 5,609,636; 5,425,772; 4,878,915; 4,501,269; 4,961,240 and 5,055,104.
The following patents disclose Adjustable Inter-Body Fusion devices: U.S. Pat. Nos. 5,782,832; 5,766,199; 5,702,455; 5,609,635; 5,336,223; 5,306,310.
The present invention overcomes the disadvantages represented by the prior art by not requiring drilling procedures for threaded engagement of adjacent vertebrae and subsequent end plate preservation. It restores and preserves the disc inter-vertebral space with the proper curvature of the spine. As taught by this invention, the methods and devices for insertion following disc removal requires no specialized surgical technique and allows for precise placement of the device and subsequent re-establishment of the proper inter-vertebral space and lordosis by either an anterior or posterior surgical approach. Further, this invention permits precise implant size to fit within the space allowed and not endanger or damage adjacent structures. Hence, incorrect implant size selection and the need for a variety of implant sizes is eliminated. An added advantage is, if removal is necessary it would not result in iatrogenic destruction of the adjacent vertebrae. Also, spinal stability is obtained without the use of threads since such threads may adversely affect the vertebrae themselves.
The present invention is an inter-space implant utilized to replace a damaged disc. The present invention is clearly an improvement over the prior art providing an implant prosthesis intrinsically participating in this fusion process, self-stabilizing to the spinal segments, consistent with conventional methods of disectomy and uniquely and novel consistent with the preservation of the integrity of the adjacent vertebrae.
The present invention comprises an artificial implant for the purpose of which is to aid in and directly cause bone fusion across an inter-vertebral space following the removal of a damaged disc. Said prostheses are biocompatible, structurally load bearing devices, stronger than bone, capable of withstanding the forces generated within the spinal inter-space. They have a plurality of openings of specific size which can be filled with fusion promoting material by inducing bone growth and osseous integration with the adjacent vertebrae forming a bony bond to the implants and each other. The implant bone-contacting surface may be textured, designed or otherwise treated by any known technologies to achieve bone in-growth and fusion to the implants to enhance stability of the implant and to expedite the fusion. The improved devices are configured and designed so as to promote their own stability within the vertebral inter-space to resist dislodgment and stabilize the adjacent vertebrae.
The present implant is made of a biocompatible material and has means if desired for increasing osseous integration, controlling hemostasis and preventing infection. It establishes proper spinal curvature or lordosis and kyphosis and capable of reducing a vertebral listness (a forward or backward translation of one vertebrae upon another as well as lateral misalignment of said vertebrae). It gives increased safety and precision which provides complete and easy visualization of the structures involved and adjacent vital structures (e.g. organs, neural structures and blood vessels and related bony surfaces). It also eliminates the need for a second surgical procedure to harvest bone. It also provides the method and material that is resorbable for additional means of stabilization to be used in conjunction with the implant prosthesis for certain conditions that require additional stabilization for osseous integration. It may be used in distraction osteogenesis procedures in order to increase bone length and/or for inducing bone growth and osseous integration of the implant, and for controlling hemostasis and pain and preventing infection during and following the surgical procedure allowing for an increased opportunity of success.
Procedure for Implant
A conventional disectomy is performed and the vertebral end plates are roughened in preparation for use of the implant prosthesis of the present invention.
In an anterior cervical device implantation a short transverse incision is made across the front of the neck and off-center, preferably to the right of the midline and directly over the diseased or otherwise disc being replaced. The platysma muscle is dissected and split and the sternocleido-mastoid muscle with the carotid sheath is protected and retracted laterally. The esophagus, trachea and associated midline structures are protected and retracted medially, thus exposing the anterior aspect of the cervical spine. The disc involved is identified and removed by known, acceptable and conventional surgical methods. The adjacent vertebral end plates are gently scraped free of any remaining cartilage until diffuse fine punctuate decortication is achieved. The dimensions of the inter-space are then measured in mild distraction and compared with the stereo-tactic pre-surgical x-ray diagnostic procedures and video imaging devices which helps to determine the exact intra-discal space to be restored relative to the vertebrae involved and the undamaged disc space that exists inferiorly and superiorly to the vertebrae involved. The appropriate device or devices are selected for insertion with a specially designed device that establish the necessary space for insertion behind the anterior lips of the vertebrae. The device is activated for establishing the desired inter-vertebral space and said device is locked at the desired height. Alternatively, the prosthesis may be a single, double or multiple activated device so as to properly provide stability and the proper curvature or lordosis of the spine. Harvested bone or bone fill material commonly employed is packed into and around the implant. Alternatively a new bone fill material is provided that is a polymer capable of being polymerized into a desired shape and size via being a resorbable biocompatible photo-initiated polymer and cured via visible light. In certain situations of trauma and disease additional stabilization is required and a resorbable biocompatible photo-initiated polymer rod or plate and screws may be utilized and to be attached to the vertebrae involved as well as healthy vertebrae above and below the damaged site. Guide plates are provided for drilling holes to affix the plate and or rod to the vertebrae with the necessary screws. In extreme cases the additional stabilization may employ currently available rigid devices for such purposes. All areas are inspected and the wound is then closed in the routine manner. A further biocompatible resorbable photo-initiated polymer is provided to control hemostasis as well as controlling post-operative pain or infection. The devices may also be used in other areas of the spine, such as the thoracic and lumbar regions, utilizing both the anterior or posterior surgical approaches as selected by the surgeon.
It is the object of the present invention to provide for a means of achieving fusion of the inter-vertebral space and stabilization as a single procedure by a means consistent with the conventional method of disectomy and re-establishing the ideal and normal pre-existing disc inter-space.
It is another object of the present invention to provide for a means of achieving an inter-space fusion and stabilization that is easier, quicker, safer and entails less blood loss than other known means.
It is another object of the present invention to provide for a means of achieving a one stage inter-space fusion and stabilization with minimal damage and less removal of bone from the surface of the adjacent vertebrae than other known means.
It is another object of the present invention to provide for a method and device for inter-vertebral arthrodesis and stabilization and establishing the normal and pre-exiting inter-vertebral space in an easy, quick, safe and precise manner and in addition the entire procedure is performed under direct vision and may be further guided by optical imaging computerized devices.
It is another object of the present invention to provide for a method and device of inter-vertebral arthrodesis and stabilization that allows for the inter-vertebral space to be adjusted and of variable sizes unlike any other known means and with greater simplicity and accuracy than any other known means.
It is another object of the present invention to provide for a modular prosthesis having similar and multiple attachments that allows for insertion through a small opening and then to reconstitute an inter-space occupying device much larger than would be normally inserted.
It is another object of the present invention to provide for a method and device that precisely fits the contours of any inter-space without the need to sacrifice any vertebral bone to accommodate the prosthesis and can be inserted from an anterior or posterior surgical approach if desired.
It is another object of the present invention to provide for an implant that has means for osseous integration with the adjacent vertebrae and said device having additional means to act as a shock absorber when extremely heavy forces are exerted upon said device.
It is another object of the present invention to provide for a method and device that reestablishes the normal lordosis of the spine in a simple and precise manner.
It is another object of the present invention to provide a method and biocompatible material for inducing bone growth that is easier to use than any other known materials for this purpose and can readily be shaped into a desired form and resist dislodgment. This material may also act over a prolonged period of time by being time released for this purpose.
It is another object of the present invention to provide a biocompatible material and method for use in controlling hemostasis thereby enhancing the opportunity of success for osseous integration in individuals with abnormal clotting times. The hemostatic agent may also act over a prolonged period of time to further control post- operative bleeding, especially in individuals with poor clotting times, by being time released for this purpose.
It is another object of the present invention to provide a material and method for controlling post-operative pain following the surgical procedure, and said material may be time released locally over a period of time for this purpose.
It is another object of the present invention to provide a material and method for preventing and controlling infection following the surgical procedure and said material may be time released locally and/or in combination with systemic drugs for this purpose.
It is another object of the present invention to provide a material and method for use of time released anti-tumor drugs or radiation seeds that may control or eradicate tumors related to the area of uses of said invention.
It is another object of the present invention to provide a method and device for use in distraction osteogenesis procedures unlike any other known devices and method currently employed.